1. Field of the Invention
The present invention relates to the use of liquids and in particular solid substances as precursors of gas phase processing of, e.g., thin films. Particularly, the invention concerns a method and an apparatus in which liquid or solid matter is vaporised in a reactant source and the vaporised reactant is fed into the reaction chamber of a gas phase process for example for growing a thin film on the substrate of a semiconductor device.
2. Description of Related Art
During processing of semiconductor wafers various gases are fed into the reaction chamber. Typically the gases employed are present in gaseous form in the reactant source. They are also often gaseous at ambient (i.e. normal) pressure and temperature. Examples include nitrogen, oxygen, hydrogen, and ammonia. In some cases, gases of source chemicals which are liquid or solid at ambient pressure and temperature are used. These substances may have to be heated to produce sufficient amounts of gases for the reaction. For some solid substances, the vapour pressure at room temperature is so low that they have to be heated even up to several hundred degrees centigrade.
Generally the solid precursor is present in the form of a powder possibly may abundantly fines, which make the solid matter into a dusting powder. The dust can easily be conducted along with the reactant and the small particles and fines can be conveyed by diffusion. If the particles end up on the substrate they may cause small pin point sized holes and deformations in the thin film which can affect the operation of the film.
Conventionally, the solid precursor material has been placed in open containers which communicate with the reaction chamber. No means for separating dust from vaporised reactant gases has been provided. The containers are usually fitted inside the same pressure shell as the reaction chamber. As a result, the size of the pressure shell or vacuum vessel has to be increased. Further, the chemical is contacted with air during loading and maintenance operations which may lead to contamination of the precursor material. During loading of the chemical, the vacuum of the reactor chamber is broken. When the reactant source is located inside the reactor, there will also be constant evaporation of the chemical and at least some of the vaporised precursor will be drained via an outlet channel and some material will be deposited on the channel walls.
It is an aim of the present invention to eliminate the drawbacks of prior solutions and to provide an entirely novel method and apparatus for feeding gas phase pulses from liquid or, in particular, solid sources into a gas phase reactor.
It is a further aim of the invention to provide a novel reactant source assembly for generating a gas phase reactant flow.
These and other objects, together with the advantages thereof over known processes and apparatuses which shall become apparent from the following specification, are accomplished by the invention as hereinafter described and claimed.
The present invention is based on the idea separating the production of reactant gas from the use of the gas in a gas phase process. Basically this concept is implemented by providing two separate units, viz. a reactant source and a reaction chamber which are located in separate vessels each inside a pressure shell of its own. Thereby the units can be separately and individually evacuated to allow for independent operation and maintenance of both.
It is preferred to provide the reactant source with a gas inlet for feeding gas into the reactant source and a gas outlet for withdrawal of gaseous reactant. Thereby, carrier gas can be fed into the reactant source and the necessary flow of gas from the reactant source to the reactor can be achieved by means of the carrier gas which contains evaporated reactant.
According to a particularly preferred embodiment, the reactant source comprises a first container having an opening and which is placed within a pressure shell and heated to the vaporising temperature by using heating means fitted within the pressure shell. The vaporised reactant is conducted from the container through a first purifier to remove impurities contained in the vaporised reactant; the vaporised reactant is collected in a gas space: and the gas phase reactant is fed from the gas space into the gas phase reaction chamber via a first conduit interconnecting the reactant source and the reactor.
Based on the above, the invention provides a novel reactant source assembly for generating a gas phase reactant flow. It comprises a first container having an opening and containing liquid or solid reactant matter; a second container having a gas tight container wall enclosing the first container and defining a gas space around the first container; at least one first gas nozzle fitted in the container wall of the second container for feeding gas into the gas space; and at least one second gas nozzle fitted in the container wall of the second container for withdrawing reactant vaporized from first container and collected in the gas space.
More specifically, the method according to the invention is mainly characterized by what is stated in the characterizing part of claim 1.
Considerable advantages are obtained by the present invention. The invention makes it possible to change and load new reactant chemical without breaking the vacuum of the reaction chamber. Contact between the reactant chemical and air can be prevented. No separate heating of the conduit interlinking the reactant source and the reaction chamber is needed. A constant flow of reactant gas can be ensured. Dust can efficiently be removed from the reactant gas. The modular concept of the invention can be broadened so as to allow for a plurality of reactant sources connected to the same reactor.
The invention can be applied to a large number of solid precursors, such as metal compounds, such as metal halides, organometal compounds comprising metal-to-carbon bonds, metalorganic compounds, which do not comprise a metal-to-carbon bond but which contain carbon (e. g. thd compounds), and elemental metals.
Next the invention will be examined more closely with the aid of a detailed description and with reference to a working embodiment.